The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In wireless communications, a transmitted signal (e.g. radio signals) may be received at a wireless receiver via multiple transmission paths. In other words, the wireless receiver includes an antenna that may receive the same transmitted signal via multiple paths. This tendency to receive the same signal via multiple paths is referred to as “multipath.”
Multipath may cause reception errors and decrease quality in wireless communications. For example, multipath may cause intersymbol interference (ISI). A signal received via one of the paths may be out of phase with the same signal received via another one of the paths. Signals that are received in phase with each other result in a stronger signal at the wireless receiver. Conversely, out of phase signals result in a weak or fading signal at the wireless receiver (i.e. result in multipath fading).
Referring now to FIG. 1, a wireless receiver 10 may include a rake receiver 12 to compensate for the effects of multipath fading. A radio frequency (RF) front end module 14 receives a wireless signal 16 from an antenna 18. The rake receiver 12 receives the wireless signal 16 from the front end module 14. The rake receiver 12 decodes each individual path independently and combines the strongest transmission characteristics of each of the paths to generate an output signal 20.
The wireless receiver 10 includes a frequency phase loop module 22 and a timing loop module 24. The frequency phase loop module 22 estimates a frequency offset based on the output signal 20. The timing loop module 24 determines a sampling frequency difference between a wireless transmitter (not shown) and the wireless receiver 10.
Referring now to FIG. 2, the rake receiver 12 includes a plurality of fingers 30-1, 30-2, 30-3, . . . , and 30-N (referred to collectively as fingers 30) and a plurality of corresponding delay modules 32-1, 32-2, 32-3, . . . , and 32-N (referred to collectively as delay modules 32). The fingers 30 receive multipath signals 34 via a corresponding transmission path. Each of the fingers 30 despreads a corresponding one of the multipath signals 34. The delay modules 32 adjust time offsets of the multipath signals 34. A combining module 36 combines the adjusted multipath signals 34 and generates an output signal 38. The combined output signal 38 may have a higher signal-to-noise ratio than any of the individual multipath signals 34.